Hi Michel,
I'm also transitioning from a Palm Tungsten to an IPT. I agree the others' comments could have been more helpful. Anyway, I have Documents To Go on my Palm and they have announced they are in the process of producing a version for the IPT and they may have some of the apps you are looking for.
1. I use the Palm Desktop for my To Do's and tasks, and still do, I haven't found a better app on the app store. I was also hoping for a more positive response from the other posters.
2. I have seen some "Memos" on the app store, but have not tried them, try under Utilities or Productivity or Business headings in the app store.
3. Same as in 2. above.
4.I don't know if you have Documents To Go on your Palm, but if you do, I think you may find it easier to make a template up in Excel on your computer and copy it over to your Palm, like I did. The Word and Excel files are quite small on the Palm and I found these apps were invaluable to me, together with Filemaker Mobile, which again, I understand the new Filemaker 10 is supposed to work on the IPT.
I did try a free shopping list app called "ShopShop", but it is very poor. If you want an app that you can use on the go from your IPT, then I suggest you try this one for now, because I have not found any apps that allow you to edit any Word or Excel files on the IPT, only to view them, so I am waiting for Dataviz (who make Documents To Go) to finish their IPT version.
If you have time to make a list in Excel on you computer, there are 2 apps that I've tried where you can copy Word or Excel files to your IPT, but only to view, not to edit. They are "Air Sharing" and "Flash Drive".
The app store is still very young, but slowly big apps are being written. At the moment there seems to be a shortage of real business or professional apps.
I hope you find this helpful, and I like you, will have to be patient before the app store has more mature apps like we have had the benefit of using on our Palms.
Cheers.